Disease relevance of PCK1

• Linkage studies showed that PCK1 is not tightly linked to MODY in one large pedigree and exclude this diabetes candidate gene as the cause of MODY in this family [1].
• Disregulated glyceroneogenesis: PCK1 as a candidate diabetes and obesity gene [2].
• Because the gluconeogenic pathway contributes to the fasting hyperglycemia of type II diabetes, inhibitors of PEPCK may be useful in the treatment of diabetes [3].
• Several protein-nucleic acid complexes are observed when nuclear extracts from hepatoma cells are assayed for binding to the cAMP response element found in the phosphoenolpyruvate carboxykinase-cytosolic (PEPCK-C) promoter [4].
• This transcription factor binds to cAMP-response element 1 within the PEPCK promoter and may enhance its transcription during metabolic acidosis [5].

High impact information on PCK1

• To understand the role of VAD1 in virulence, a functional genomics approach was used to identify 3 additional virulence determinants dependent on VAD1: PCK1, TUF1, and MPF3, involved in gluconeogenesis, mitochondrial protein synthesis, and cell wall integrity, respectively [6].
• Whereas our study suggests the location of a susceptibility locus for early onset NIDDM in the PCK1 gene region, further investigation in larger data sets is required to confirm these results and assess the role of other regions on chromosome 20q in human NIDDM [7].
• Several candidate genes for non-insulin-dependent diabetes mellitus (NIDDM) map on chromosome 20, including the phosphoenolpyruvate carboxykinase gene (PCK1) and one of the maturity onset diabetes of the young genes (MODY1) [7].
• PCK1 was mapped to human chromosome 20 using DNA from a panel of reduced human-hamster somatic cell hybrids [1].
• A simple tandem repeat DNA polymorphism in the 3'-untranslated region of the mRNA was characterized and used to localize PCK1 relative to the gene responsible for a form of non-insulin-dependent (Type 2) diabetes mellitus called maturity-onset diabetes of the young (MODY) [1].

Chemical compound and disease context of PCK1

• We sequenced the promoter and coding regions of PCK1 encoding cytosolic phosphoenolpyruvate carboxykinase from genomic DNA of subjects with type 2 diabetes mellitus (DM) [8].
• Since these are the major regulatory hormones controlling glucose homeostasis, and because increased hepatic glucose production is one of the characteristics of non-insulin dependent diabetes mellitus (NIDDM), investigators have speculated that the regulation of PEPCK gene expression may be defective in patients with NIDDM [9].
• Here, we show that treatment of H4IIE hepatoma cells with the synthetic glucocorticoid, dexamethasone (dex), induces the accumulation of glucocorticoid receptor, as well as many transcription factors, coregulators, and RNA polymerase II, on the PEPCK gene promoter [10].
• Treatment of ob/ob mice with 30 mg/kg b.i.d. A-769662 decreased hepatic expression of PEPCK, G6Pase, and FAS, lowered plasma glucose by 40%, reduced body weight gain and significantly decreased both plasma and liver triglyceride levels [11].
• In acidosis, the mRNA of kidney system N amino acid transporter SNAT3 (SLC38A3/SN1) showed a strong induction similar to that of PEPCK, whereas all other tested mRNAs encoding glutamine or glutamate transporters were unchanged or reduced in abundance [12].

Biological context of PCK1

• This assignment was confirmed using fluorescence in situ chromosomal hybridization which localized PCK1 to chromosome 20, band q13.31 [1].
• In contrast, a second PPARgamma/RXR-binding element centered at -446 bp, PCK1, is not involved in adipocyte specificity because inactivation of this site did not affect transgene expression [13].
• The aim of this study was to identify genetic polymorphisms in potential candidate genes for type 2 diabetes by sequencing all exons in the PCK genes (PCK1 and PCK2), and examining the association with type 2 diabetes and diabetic phenotypes in a Korean population (775 type 2 diabetic patients and 316 normal control subjects) [14].
• RESULTS: Although no significant associations between the genetic polymorphisms in PCK genes and the risk of type 2 diabetes were detected, in further haplotype analysis, one of the common haplotypes, PCK1 ht3, revealed susceptibility to type 2 diabetes (p=0.006) [14].
• The common assumption is that mutations in PCK1 lead to excessive glucose production through hepatic gluconeogenesis [2].

Anatomical context of PCK1

• We also suggest specific quantitative metabolic traits that would accompany mutations that selectively affect PCK1 expression in adipose tissue [2].
• In human liver, PEPCK is about equally distributed in both cytosol (PEPCK-1) and mitochondria (PEPCK-2) [15].
• Finally, insulin treatment of human hepatocytes and HepG2 cells caused repression of PGC1alpha and a concomitant down-regulation of ApoCIII, PEPCK, AldoB, and OTC [16].
• The photosynthetic isoform of PEPC in the cytosol of mesophyll cells in Kranz-type C(4) photosynthesis has distinctive kinetic and regulatory properties [17].
• We demonstrated that in cultured human subcutaneous adipose tissue explants, PEPCK-C specific activity and mRNA were induced by 1 microM of the TZD rosiglitazone, respectively, about twofold in 8 h and fivefold in 5 h [18].

Associations of PCK1 with chemical compounds

• Human PCK1 encoding phosphoenolpyruvate carboxykinase is located on chromosome 20q13.2 [19].
• Our results indicate that both C/EBP proteins and CBP participate in the regulation of PEPCK gene transcription by thyroid hormone [20].
• PEPCK catalyzes the rate-limiting step in the metabolic pathway that produces glucose from lactate and other precursors derived from the citric acid cycle [3].
• Glucagon (acting via cyclic AMP (cAMP)) and glucocorticoids stimulate PEPCK gene transcription, whereas insulin has the opposite effect [9].
• Treatment of mice with phenobarbital or TCPOBOP resulted in decreased hepatic mRNA levels of the reported genes down-regulated by CAR, including Cyp7a1 and Pepck [21].

Physical interactions of PCK1

• Thus, AUF1 binds to multiple destabilizing elements within the 3'-UTR that participate in the rapid turnover of the PEPCK mRNA [22].
• We found that the RA receptor can bind to sequences within the PEPCK-TRE and contribute to RA responsiveness of the PEPCK gene [23].

Regulatory relationships of PCK1

• Furthermore, PGC-1alpha phosphorylation by p38 was necessary for FFA-induced activation of the PEPCK promoter [24].
• The overexpression of the dominant-negative CREB prevented FFA-induced activation of the PEPCK promoter [24].
• These results show that ATF-2 can stimulate transcription of the PEPCK-C promoter and support a role for stress inducible kinases in the maintenance of PEPCK-C expression [4].

Other interactions of PCK1

• Moreover, electrophoretic mobility shift experiments indicated that, unlike PCK2, PCK1 is not selective for PPARgamma/RXR binding [13].
• We have utilized Southern blot analysis on human/rodent somatic cell hybrids to map the human homologues of both of these genes, PCK1 and CHRNA4, to human chromosome 20 [25].
• Using vectors with deletions in the PEPCK promoter, we identified a single T3 response element (TRE) between positions -332 and -308 [26].
• Therefore, we analyzed the human tissue localization and cellular distribution of FBPase and PEPCK immunohistochemically [27].
• CCAAT-enhancer-binding protein alpha (C/EBP alpha) is required for the thyroid hormone but not the retinoic acid induction of phosphoenolpyruvate carboxykinase (PEPCK) gene transcription [23].

Analytical, diagnostic and therapeutic context of PCK1

• Fluorescence in situ hybridization with YAC DNA further localized PCK1 to subband 20q13.2 [19].
• Yeast two-hybrid assays indicate weak interactions between MDH2 and yeast phosphoenolpyruvate carboxykinase (PCK1) and between MDH2 and fructose-1,6-bisphosphatase (FBP1) [28].
• Additional evidence was obtained for interaction of MDH2 with PCK1 using Hummel-Dreyer gel filtration chromatography, and for interactions of MDH2 with PCK1 and with FBP1 using surface plasmon resonance [28].
• Western blots revealed two PEPC-specific bands in C(3) and C(4) leaf extracts; the lower band dominated in the C(4) and underwent post-translational phosphorylation in the light as determined by immunological studies [29].
• Site-directed mutagenesis of Lys600 in phosphoenolpyruvate carboxylase of Flaveria trinervia: its roles in catalytic and regulatory functions [30].

References